In subsea construction and repair activities it is often required to attach one or more buoys to heavy structures or pieces of equipment to facilitate subsea emplacement. In such a way the effective underwater weight is reduced to a manageable value, minimizing the chances of damage during subsea installation and minimizing surface crane requirements after launching and during lowering and placement of the structures. Connections between the buoys and the structure are often made with bolts, eyes, hooks and other hardware. If it is necessary to release the buoys, this can be done with the direct help of divers, but it is considered safer to release the connections remotely, using explosives or acoustically triggered release mechanisms. Unfortunately, actively triggered mechanisms can be triggered accidentally and can fail to trigger when needed.
The use of such buoys is particularly attractive for laying a pipeline in deep water from a laybarge. It has been the general practice in the art to provide stability and support to a pipestring during an offshore pipe laying operation by means of a stinger, which is a mechanical structure extending from a hinged joint at the rear of the barge to or toward the submarine floor. However, a stinger must be quite long for laying a pipeline in deep water, for example 200 to 1000 feet or more. As a result such a stinger is expensive, difficult to control, and vulnerable to weather damage. Accordingly, in laying a deep water pipeline, buoys are used as an alternative to stingers for supporting the pipestring during the pipelaying operation. U.S. Pat. No. 3,727,417 discloses a system for laying underwater pipelines using buoyant spheres connected by cables which are attached to the pipeline at calculated intervals. As the pipeline is laid, it forms a sloping curve, and as the pipeline reaches bottom, the spheres are released and float to the surface. U.S. Pat. No. 3,620,028 discloses a similar system for laying underwater pipelines wherein cable-connected floats are attached to the pipeline at selected intervals; a release mechanism disengages the floats as the pipeline reaches the bottom, and the floats rise to the surface where they are collected. Other pertinent art includes U.S. Pat. Nos. 3,262,275; 3,765,185; 3,795,115; 3,835,655; 3,909,774; 3,921,562. From this art, it is evident that there is no actuation means for releasing flotation from a pipestring which is both inexpensively constructed and fully reliable to disengage a pipeline at a selected water pressure. However, such actuation means is provided by the present invention, as will be evident from the following disclosure.